The present invention relates to a fluid-operated ram comprising a housing, an axially guided striker body, a pressure fluid cylinder arranged on the housing or in the striker body, coaxially with respect thereto and divided by a working piston reciprocably arranged in the cylinder in a first and a second chamber. A piston rod connects the working piston with the striker body within the housing. Passage means connect both chambers of the cylinder with a source of pressure fluid and at least the first chamber, which increases in volume the movement of the striker body during its active stroke is associated with a tank for receiving the pressure fluid. The ram comprises further control devices including a valve slide limitedly movable in the housing coaxial to the piston rod between a first position in which at least one chamber of the cylinder is connected with a source of pressure fluid and a second position connecting the chamber with the tank for receiving the pressure fluid and devices for moving the valve slide to the second position dependent on the position of the striker body.
Such a ram is disclosed in the German Auslegungsschrift 1,634,298. This ram has a pressure fluid filled space in the piston rod, a hollow fluid-filled plunger piston coaxially guided through the working piston and extending into the hollow space in the piston rod and reversing the valve slide in dependence on the movement of the working piston. For this purpose the hollow space in the piston rod is connected over the plunger piston and passages in the housing with two storage cylinders, subdivided by a movable piston and over the working piston and bores, opened only in the lower end position of the working piston, with the upper chamber of the cylinder. Thereby, the fluid enclosed in the hollow of the piston rod and of the plunger piston will, during upward movement of the working piston, reverse the valve slide against the pressure force acting permanently on the upper end of the latter. This known construction has, however, the disadvantage that the plunger piston, which is integrally connected with the valve slide, is permanently in contact with the working piston so that blows occurring during the active stroke of the striker body on the latter are transmitted to the working piston fixedly connected to the striker body and thereby transmitted to the sensitive control devices which will lead to undesired vibrations and break down of the latter. Since the size of the control devices is not correspondingly increased at increasing size of the ram, the control devices are relatively small, fragile parts, so that such blows onto the control devices will be the more damaging the greater the ram is dimensioned. Since in the above-mentioned known ram the plunger piston serving as valve slide is built into the pressure fluid cylinder and the working piston and since the remaining control elements and connecting channels are integrated in the housing of the ram, it is necessary during operating trouble to bring the whole ram into the work shop and there disassemble the same. This is evidently expensive and time consuming with rams of large size.
While fluid operated rams are also known in the art in which the control devices are arranged spaced from the housing of the ram and respectively connected to the latter by pressure fluid conduits, these known rams have the disadvantage of requiring long fluid pressure conduits from the control devices to the cylinder and that the connection of the fluid pressure conduits to the control devices and to the housing of the ram may be loosened by vibration, which is especially detrimental at off-shore operation of the ram in which the ram is located under water.